Details

Autor(en) / Beteiligte

• Woodcock, Jeremiah W
• Wright, Roger A. E
• Jiang, Xueguang
• O'Lenick, Thomas G
• Zhao, Bin

Titel

Dually responsive aqueous gels from thermo- and light-sensitive hydrophilic ABA triblock copolymersElectronic supplementary information (ESI) available: Temperature ramp for a 10.0 wt% aqueous solution of ABA-1; frequency dependences of G′ and G′′ of a 10.0 wt% aqueous solution of ABA-3 after UV irradiation at 41, 48, and 65 °C; temperature ramps for aqueous solutions of ABA-3 with concentrations of 14.2, 10.0, 6.0, 4.0, and 3.0 wt%; temperature ramps for aqueous solutions of irradiated ABA-3 wi

Erscheinungsjahr

2010-07

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• We report in this article the synthesis of a series of thermo- and light-sensitive hydrophilic ABA linear triblock copolymers, poly(ethoxytri(ethylene glycol) acrylate- co - o -nitrobenzyl acrylate)- b -poly(ethylene oxide)- b -poly(ethoxytri(ethylene glycol) acrylate- co - o -nitrobenzyl acrylate) (P(TEGEA- co -NBA)- b -PEO- b -P(TEGEA- co -NBA)), with various NBA molar contents and the study of sol-gel transitions of their aqueous solutions. The copolymers were prepared by ATRP from a difunctional PEO macroinitiator; the polydispersity indexes of all polymers were <1.2. We demonstrated that a 10.0 wt% aqueous solution of a triblock copolymer with a NBA content of 9.3 mol% in the thermosensitive blocks underwent a thermo-induced reversible sol-gel transition and a UV-triggered gel-to-sol transition at a constant temperature. The UV-irradiated solution again can undergo a temperature-induced sol-gel transition but at a higher temperature. The thermo-triggered sol-gel transitions stemmed from the formation of a 3-dimensional network with the dehydrated thermosensitive blocks being associated into hydrophobic cores and the central PEO block forming bridges among micelles. Exposure to UV light cleaved hydrophobic o -nitrobenzyl groups, raised the LCST of thermosensitive blocks, and thus triggered a gel-to-sol transition at a constant temperature. Rheometry was employed to study the sol-gel transitions and gel characteristics. In addition, we studied the effects of polymer concentration and NBA content on sol-gel transition temperature ( T sol-gel ) and gel properties before and after UV irradiation. The T sol-gel increased with the decrease of polymer concentration; the critical gelation concentration for the triblock copolymer with a NBA content of 9.3 mol% was between 3 and 4 wt% before UV irradiation and between 5 and 6% after photocleavage of o -nitrobenzyl groups. The change of T sol-gel was in general larger for the copolymer with a higher NBA content after UV irradiation. A 10.0 wt% aqueous solution of a thermo- and light-sensitive ABA triblock copolymer can undergo multiple sol-gel/gel-sol transitions in response to temperature changes and UV irradiation.